Description
5-Carboxyfluorescein NHS Ester (5-FAM-SE) – High-Performance Fluorescein Labeling Reagent
5-FAM-SE is a single-isomer, amine-reactive derivative of fluorescein designed for covalent labeling of proteins and alkylamino-modified nucleic acids. Featuring high quantum yield, excellent water solubility, and strong absorption at 495 nm, it is the fluorophore of choice for applications such as flow cytometry and confocal laser scanning microscopy. Its NHS ester moiety reacts with primary amines to form stable thiourea linkages, enabling robust and reliable fluorescence tagging.
The excitation spectrum of 5-FAM-SE closely matches the 488 nm line of argon-ion lasers, making it especially well-suited for standard fluorescence detection platforms. The reagent is provided as an orange solid and remains stable when stored dry and protected from light at −20 °C.
Performance Highlights
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Single-isomer NHS ester ensures consistent conjugation
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High absorptivity and fluorescence quantum yield
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Ideal spectral match for 488 nm excitation lasers
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Excellent solubility and low risk of precipitation after labeling
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Compatible with proteins and alkylamino-modified oligonucleotides
Properties
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Molecular Weight: 473.4 g/mol
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Empirical Formula: C₂₅H₁₅NO₉
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Absorption [λmax]: 495 ± 3 nm
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Emission [λmax]: 519 ± 3 nm
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Extinction Coefficient (ε): ≥ 74,000 M⁻¹·cm⁻¹
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Reactive Moiety: NHS ester (reacts with 1° amines to form stable thiourea linkage)
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Solubility: DMF, DMSO, Methanol
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Appearance: Orange solid
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Storage: –20 °C, dry, protect from light (especially in solution)
Applications
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Flow cytometry (FACS)
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Confocal laser scanning microscopy
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Fluorescent labeling of antibodies and proteins
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Bioconjugation of alkylamino-modified DNA/RNA
Why Choose 5-FAM-SE?
5-FAM-SE offers exceptional labeling consistency, brightness, and compatibility with commonly used detection systems. With its high water solubility and well-characterized fluorescence profile, this reagent provides a reliable solution for researchers in molecular biology, diagnostics, and imaging. The single-isomer format ensures precise, reproducible results across a range of protein and oligo labeling protocols.
